One technique that is well known for fabricating preforms from which lightguide fibers are drawn is known as the Modified Chemical Vapor Deposition (MCVD) process and is described in U.S. Pat. No. 4,217,027 which issued on Aug. 12, 1980 and is hereby incorporated by reference. Lightguide preform fabrication starts with a chemically cleaned tube of fused quartz which is rotated in a glass working lathe. A surface mixing oxy-hydrogen torch repeatedly moves along the length of the tube in one direction resulting in a hot zone (approximately 1400.degree. to 1800.degree. C.) moving therealong. Chemical vapors are directed into the rotating tube as the torch traverses its length, resulting in the deposition of uniform core layers of fused doped silica on the inside of the tube.
Multiple layers are deposited in this fashion to produce the desired tube-to-core mass ratio and a desired refractive index profile. Anywhere from 50 to 100 traversals of the torch are made, and the amount of dopant used on each pass may be varied, increasing the refractive index in each successive deposited layer to fabricate a graded index preform or the dopant level may be maintained constant in each layer to form a step index preform. The tube, with the deposited layers therein, is then collapsed into a solid rod preform by elevating the temperature of the torch to approximately 2,000.degree. C. as it moves along the length of the tube in several passes.
One type of torch used in the above fabrication process, for both deposition and collapse, is comprised of a multitude of small diameter hollow tubes having their first ends forming an arcuate array and their second ends communicating with a supply of gas, as shown in U.S. Pat. No. 4,231,777 which is assigned to the instant assignee. Oxygen exits through the tube ends while hydrogen passes through the gaps between the tubes. This torch has been found to be most effective in fabricating lightguide preforms. However, such a torch is expensive to manufacture and troublesome to repair. Additionally, it is difficult to control the velocity of the gases emanating from the torch due to variations in the diameters of the tubes.
Accordingly, there is a need for a relatively inexpensive torch which can be easily assembled or disassembled to repair. Additionally, the torch should provide uniform gas velocities.